Tumor growth patterns in multiple myeloma.

Serial changes in tumor mass were evaluated in 61 patients with multiple myeloma who had received intermittent courses of melphalan-prednisone until death. The variations in the kinetics of tumor reduction and relapse could be explained by a mathematical model based on two cell populations, one sensitive to and one resistant to chemotherapy. For all responding patients, the median tumor halving-time was 1.3 months and the median doubling time was 2.9 months. The duration of a constant tumor mass during remission was brief in most patients. A larger fraction of resistant cells prior to therapy was associated with a slower tumor doubling-time during relapse. With a constant fractional reduction of sensitive cells and a tumor halving-time of one month or less, all cells sensitive to alkylating agents would be eliminated with 3 years of uninterrupted intermittent therapy.